1. Field of the Invention
The present invention relates to machines for carding of textile fibres, in which the flock fibres are worked in order to produce a web of fibres. In this operation, the short fibres and tangles are removed from the fibres, which are stretched and placed in parallel in a web of fibres, which is disposed on the covering of the drum of the carder, from which the web of fibres is collected by a rotary detachment cylinder with a suitable covering, which is commonly known as a doffer, and is then transferred by another doffer to a compactor unit and to a drawing unit, in order to produce a strip of fibres.
More particularly, the present invention relates to the method and the device in which the web which is detached from the carder is transformed into a strip, and is subjected to controlled and progressive drawing, in order to obtain a constant, predetermined yarn count.
2. Discussion of the Background
In order to assist understanding of the technical aspects involved in the carding, reference is made to a diagram of a collection and drawing unit according to the known art, which is described in European patent application no. 775,768 in the name of the same applicant, illustrated in FIGS. 1 and 2, which show respectively a schematic lateral view and a plan view of the collection and drawing unit.
The detachment cylinder, or doffer, of the carder, is indicated as 1, and on the latter the web 2 of fibres is carried to the unloading cylinder 3, and is conveyed to the compactor unit 4, which consists of a pair of smooth rotary cylinders 5,6, with a substantially horizontal axis, which compact the web 2, which still has a transverse dimension which corresponds to that of the carder, and transfer the web to the subsequent belt conveyor. The compactor unit 4 works at a speed which is the same as, or slightly greater than that of the web 2 which is obtained from the unloader 3.
The belt conveyor 10 is in a position which is integral with the collection unit of the web 2 described hitherto, and consists of a pair of belts 11 in a loop, which are opposite, and are guided by means of rollers 12 which have a substantially vertical axis, rotate on pins 13, and are provided with rotary drive 14, by means of their own motor, or by motion derived from other units, in a known manner. The said belts 11 extend along the entire front of the collection unit, as far as lateral return rollers which are not shown in the figure for the sake of simplicity, and leave a central gap 15. The belts are actuated such as to be moved, in the area which is provided for the web of fibres obtained from the compactor unit 4, from the sides towards the centre, in order to concentrate and convey the web 2 of fibres into a strip 16, which has a width which corresponds to the gap 15 between the two belts 11. The stretched web 2, which has been condensed into the form of a strip 16, is then yielded to the drawing unit 20, and the linear speed of transfer of the fibrous body is substantially maintained from the compactor unit 4 to the drawing unit 20.
The equipment of the drawing unit 20 is mounted on a mobile carriage, which can move longitudinally, towards and away from the preceding collection unit. This movement is obtained, for example, by placing the equipment of the drawing unit on a transverse frame 21, which slides forwards and rearwards according to the arrow 22 on guides, and is piloted by a double-effect hydraulic cylinder, which is not shown in the figure for the sake of simplicity.
The drawing unit comprises a body in the shape of a funnel 30, which receives the fibres conveyed by the belts 11 in order to form the strip 16, and admits and guides them to the two pairs of cylinders downstream, which carry out the drawing of the strip 16. Of these pairs of cylinders, a first pair of cylinders or rollers 31 and 32 with a horizontal axis comprises the upper roller 31, which is smooth and idle, and is pressed against the roller 32 beneath by means of an adjustable thruster 33 on its shaft 34. The roller 32 is embossed in a transverse direction, and is rotated with a specific drive ratio in a known manner, for example with a pulley and belt drive system, by means of the motor 35. According to the known art, and in general, the first pair of rollers 31,32 works at a linear speed which is slightly greater than that of the strip which is released by the belt conveyor 10, via the funnel 30.
The second pair of cylinders or drawing rollers comprises the roller 38, which is also smooth and idle, and is pressed against the roller 39 beneath, similarly to the first pair of cylinders. The roller 39 is also worked on its surface, and is actuated such that it is driven at a linear speed which is greater than that of the roller 32, according to a ratio which is adjustable, and greater than 1, which gives rise to the drawing, i.e. to the elongation of the strip, which is conveyed between the two pairs of rollers. In other words, the second pair of cylinders 38,39 is actuated such as to be driven at a specific linear speed, which is greater than that of the first pair of cylinders 31,32. Owing to the effect of the linear speed difference between the rollers upstream which release the body of fibres, and the rollers downstream which draw this body towards them, the fibres which are drawn downstream slide relative to the fibres which are retained upstream, and give rise to elongation and drafting of the said body of fibres. The drawing values express ratios between the linear speeds of the fibrous body input, and the fibrous body output.
For this purpose, the two pairs of drawing rollers 31,32 and 38,39 are actuated in a known manner, for example by means of the same motor 35, which is provided with a drive with belts and pulleys of a different diameter, and maintain a pre-determined, constant ratio between the linear speeds at which the strip which is gripped between the two pairs of rollers is yielded by the first pair 31,32, and drawn by the second pair 38,39. In general, the drawing values, which are established between the two pairs of rollers are between 1.0 and 2.0, whereas the values which are currently used are within the narrower interval between 1.1 and 1.5.
The strip which is thus produced and drawn is then sent to be collected in a container, for further processing. The distance between the drawing unit and the collection unit is regulated in accordance with the speed at which the carder is actuated, and with the linear speed of collection of the web, as well as in accordance with the characteristics of the fibres worked.
The problems which arise during the step according to the known art, of collection of the web and drawing of the strip of fibres, are derived substantially from the present need to operate at high levels of productivity in terms of linear production of web and strip, which, in operation, must be collected and drawn at a rate of 250-400 m per minute, and this value is destined to increase further, according to the expectations of the textile industry. High speeds of work create problems, in particular in the steps of re-starting, or in general in a transitional stage, in which the sections of web and strip between one point of collection and control and the other can be loose or slack, and can also be disposed in a highly accentuated catenary position. This occurrence is problematic because the consistency of the web and the strip is substantially reduced, since they consist of fibres in parallel. In these loose sections the web and the strip can lose continuity, owing to their own weight, and because of lack of continuity of the drawing to which they are subjected, and this can cause stoppage of production. The technical problem which is derived from these requirements of high carding productivity consists of control and recovery in good time of the loose sections of the web and strip, such that the latter are kept satisfactorily taut even in the transitional and starting steps.